Venting the doors is the easy way. Crew can also do it if there's less fire than this.
You can also turn off power to O2 - the rooms with fire in them will run out of air a little faster than the ones without, so your crew can survive that, but it's tight.
From where you paused, I'd turn off O2 and keep trying to repair the medbay. Hole up in the medbay if that gets fixed before everyone's dying, otherwise run to the less-on-fire part of the ship and hope all the fires burn out before reaching you.